1. Field of the Invention
The present invention relates to rotary kinetic fluid motors or pumps, and more specifically to a seal between a rotary blade and a stationary shroud casing.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a turbomachine such as a rotary pump and compressor or a turbine, a plurality of rotor blades rotate within a casing having a shroud that forms a gap between the blade tip and the shroud. Since the rotor blades are exposed to high pressure, any gap formed between the blade tip and the shroud will allow for leakage of the fluid from a high pressure side to a lower pressure side. Leakage reduces the performance of the turbomachine.
In a turbine, the rotor blades are exposed to high temperatures as well as high pressures. Temperature variations will cause the rotor blades to thermally grow in length such that the tip spacing will change and rubbing can occur. Blade tip rubbing can result in hot sections on the blade tip and damage to the blade tip and casing or both.
Another problem in the prior art is that any eccentricity between the rotor disc and the casing will result in the gap increasing in certain locations during rotation. Larger gaps will allow for more leakage across the gap.
Labyrinth seals have been used to provide for a seal between blade tips and the shroud surface. However, labyrinth seals are not flexible and therefore rub when the gap spacing becomes negative. Brush seals have been used in turbomachine to seal rotating parts against stationary parts. However, brush seals wear because they brush tips make rubbing contact with the rotating part. As the brush seal wears, leakage increases across the seal.
U.S. Pat. No. 6,736,597 B2 issued to Uehara et al on May 18, 2004 entitled AXIS SEAL MECHANISM AND TURBINE discloses a gas turbine engine having a turbine with a plurality of stages of rotor blades and stationary vanes, where the stationary vanes includes seals on the tips that form a seal between the vane tips and the rotating shaft. The seal is formed of a plurality of planar plates inclined with respect to an acute angle and bent so as to float away from the peripheral surface of the rotating shaft (see column 6, line 60 of this patent). The Uehara patent uses thousands of these little plates to create a seal, and the plates extend from the stationary vane and therefore do not rotate with the shaft or rotor blades.
It is an object of the present invention to provide for an improved seal between a rotating blade and a stationary shroud to reduce leakage across the seal and improve efficiency of the turbomachine. It is another object of the present invention to provide for a seal that will allow for high eccentricity between the rotating part and the stationary part. It is also an object of the present invention to provide for a seal between the rotating part and the stationary part of the turbomachine that will wear less than the prior art and, therefore, improve on the life of the parts.